The invention discloses a speed reducer. The speed reducer comprises an input shaft, a gear set and an output shaft; the input shaft is an eccentric shaft; the eccentric shaft is connected with the gear set; the gear set comprises a shell, an outer gear and at least two inner gears; the outer gear is arranged in the shell, and is internally connected with the inner gears; one side of each inner gear is in shaft connection with the input shaft; the other side of each inner gear is connected with a connecting column of the output shaft; through driving of the input shaft, the inner gears are continuously engaged with the outer gear; and through connection of the connecting column, the transmission of the output shaft and the inner gears is continuously maintained. Through shaft connection ofthe input shaft with the inner gears and transmission of the connecting column, the speed reducer achieves zero-gap conduction and high-precision and high-stability torque conduction, and excellent practicability is achieved.